溶血磷脂酸受体（LPAR2a/2b/3）在斑马鱼后侧线原基的集体细胞迁移和MET中的作用及机制

Collective cell migration is critical for animal development, tissue repair and cancer metastasis. However, the mechanisms underlying the directional migration and morphogenesis during this process remain elusive, largely due to the difficulty to visualize this migration in vivo. The zebrafish posterior lateral line is an excellent model for studying collective cell migration. During zebrafish development, the posterior lateral line primordium (pLLP) migrates as a cohort from the head towards the tip of the tail. The pLLP undergoes a tissue rearrangement through a process called mesenchymal-epithelial transition (MET), whereby cells in the leading region gradually adopt an epithelial shape to form rosette-like structures (protoneuromasts) in the trailing region. These rosettes are then periodically separated and deposited along the trunk to form proneuromasts. In our preliminary experiments, we found that lysophosphatidic acid receptors (LPAR2a/2b/3) are highly expressed in the posterior lateral line in zebrafish embryos. Knocking down their expression resulted in abnormal rosette-like structures in the pLLP and fewer neuromasts, probably due to defects in the MET. Therefore, the aims of this proposal are: 1) Establish the zebrafish models of LPAR2a/2b/3 knocking down or mutation; 2) Identify the phenotypes in posterior lateral line development, particularly defects in collective cell migration and MET in the pLLP in these models; and 3) Determine the downstream signaling pathways of LPAR2a/2b/3 in lateral line development, and their underlying molecular mechanism. This work will not only unveil a novel, LPA-mediated mechanism for regulating collective cell migration and morphogenesis, but also provide new conceptual framework for preventing and treating cancer metastasis.

集体细胞迁移在胚胎发育、组织再生和肿瘤转移中均有重要作用，然而目前对其定向迁移和形态形成的机制仍所知甚少。 斑马鱼的侧线是一个研究集体细胞迁移的良好模型。 在胚胎发育中，后侧线原基（pLLP）通过集体细胞迁移和间充质-上皮转化（MET）在迁移路径上留下多组细胞形成前神经丘。我们在前期工作中发现溶血磷脂酸受体LPAR2a/2b/3在斑马鱼胚胎的后侧线系统高表达，下调其表达导致前神经丘发育异常，提示LPAR2a/2b/3可能参与pLLP内的MET过程。 因此本项目拟构建LPAR2a/2b/3 下调或突变的斑马鱼模型，并鉴别由此导致的侧线系统发育表型，最终确定LPAR2a/2b/3的下游信号通路及表型产生的分子机理。 该研究不仅有助于理解LPA信号通路调控集体细胞迁移和形态形成的机理，对治疗和预防某些恶性肿瘤的转移也能提供新的思路。

溶血磷脂酸受体在生理和病理状态下的细胞迁移、增殖、存活等过程中起着重要作用，然而其在侧线系统集体细胞迁移和器官发育中的作用尚不清楚。本项目研究了溶血磷脂酸受体在斑马鱼侧线系统的表达及其对侧线系统发育的作用。原位杂交显示Lpar2b表达在侧线原基（pLLP）及神经丘（NM）上。吗啡啉敲降Lpar2b 导致形成的NM和毛细胞数量显著减少。深入分析发现Lpar2b并不影响pLLP的迁移，而主要影响pLLP的细胞增殖和器官大小。有趣的是，Hippo通路的Yap1也特异表达在pLLP上，并且Yap1 敲降导致类似Lpar2b 敲降的侧线表型。进一步实验显示Lpar2b在pLLP内调控Yap1的磷酸化和活性，并且Lpar2b通过Yap1调控pLLP细胞增殖和器官大小。本项目首次发现溶血磷脂酸受体在体内通过Yap1调控听觉器官大小，具有较大的原创性和重要性。该研究成果为脊椎动物听觉器官的发育机制增添了新的内容。